There are millions of motorcycle riders in the United States. One of the loudest noises that is produced by a motorcycle is from the exhaust system. Noise levels from motorcycle exhaust systems are measured in Decibels (dB) are regulated by government agencies at all levels not to exceed certain levels.
Generally at least four things influence how loud a motorcycle engine exhaust system will be: (1) a size of the motorcycle engine; (2) a number of pistons used by the motorcycle engine; (3) a construction of an exhaust system including internal and external flow of exhaust gases; and (4) function of motorcycle (e.g., road or street riding, racing, off road, etc.).
In general, high-performance off-road two-cylinder motorcycles tend to be louder than their four-stroke road motorcycles with the same size engine because to squeeze the most power out of a two-cycle engine the exhaust system is tuned to evacuate the cylinder during the exhaust phase of a piston stroke as quickly as possible. In addition, a motorcycle with a big engine with a small number of cylinders (e.g., 1 or 2) is typically louder than a motorcycle with a smaller engine with more cylinders (e.g., 4 cylinder).
Motorcycles produced in factories that have stock exhaust systems are relatively quiet. However, many motorcycle riders desire “loud pipes,” or a loud exhaust system to attract attention, because they like the loud sound and for performance reasons. For example, many riders who buy Harley-Davidson motorcycles often replace stock or original exhaust systems with loud pipes.
There are several problems associated with loud exhaust systems on motorcycles. One problem is that motorcycles with loud exhaust systems are preferred by many riders but are a nuisance to others if a rider leaves home early in the morning or comes home late in the evening when others are sleeping.
Another problem is that a maximum noise level allowed by one governmental agency may be prohibited by another governmental agency. Since many motorcycle riders cross into and between areas regulated by different governmental agencies a motorcycle rider may have an exhaust system deemed legal in one governmental area but deemed illegal by another governmental agency.
Another problem is loud exhaust system make it difficult for a motorcycle rider to talk to a passenger or another rider. Another problem is that a loud exhaust system makes it difficult for a rider to listen to a radio, talk on a citizen band radio, cell phone, etc. Another problem is that loud exhaust system typically are higher performance than quiet exhaust systems.
Another problem is that switchable loud and quiet exhaust systems are also desirable on automobiles, trucks and marine vehicles.
Thus, it is desirable to provide an exhaust system that can be easily switched from a loud mode to a quiet mode when necessary.